NOTICE: The project that is the subject of this report was approvedby the Governing Board of the National Research Council, whose membersare drawn from the councils of the National Academy of Sciences,the National Academy of Engineering, and the Institute of Medicine.The members of the committee responsible for the report were chosenfor their special competences and with regard for appropriate balance.

This report has been reviewed by a group other than the authors accordingto procedures approved by a Report Review Committee consisting ofmembers of the National Academy of Sciences, the National Academyof Engineering, and the Institute of Medicine.

The Institute of Medicine was chartered in 1970 by the National Academyof Sciences to enlist distinguished members of the appropriate professionsin the examination of policy matters pertaining to the health ofthe public. In this the Institute acts under the Academy's 1863 congressionalcharter responsibility to be an adviser to the federal governmentand, upon its own initiative, to identify issues of medical care,research, and education. Dr. Kenneth I. Shine is president of theInstitute of Medicine.

The project was supported by funds coordinated through the NationalInstitute of Allergy and Infectious Diseases of the National Institutesof Health (contract no. NO1-AI-15130).

Additional copies of this report are available in limited quantitiesfrom:

Division of Health Promotion and Disease Prevention

Institute of Medicine

2101 Constitution Avenue, N.W.

Washington, DC 20418